In the broadest sense, the objective of this research proposal is to further our understanding of the structure and function of the gamma A type antibodies found in serum and certain non vascular fluids. The general approach is to isolate the constituent poly-peptide chains of the gamma A molecule and to determine their primary structure by amino acid sequence analysis. Emphasis will be placed on two polypeptide chains which are unique to polymeric gamma A molecules, namely J chain and secretory component (SC). In order to gain some insight into their mode of interaction and possible function, a series of reconstitution experiments are proposed in which the complexing of J chain and SC in artificially produced polymeric molecules is studied. Using both the natural polymers as well as reconstituted molecules, the susceptibility of gamma A proteins to proteolytic degradation will be investigated. In a separate series of experiments, we propose to investigate the mechanisms involved in the development and synthesis of secretory antibodies in the gastrointestinal tract of mice. The experimental approaches to be used will involve: 1) a study of the tissue localization of labeled gamma A precursor and plasma cells following systemic injection, 2) an investigation of the life span and the phenomenon of immunological memory in the secretory system, 3) an attempt to produce defects in the development of the cells in the secretory system.